text: In density functional theory, surface energy can be calculated from the following expression:
  where
  :  is the total energy of surface slab obtained using density functional theory.
  :  is the number of atoms in the surface slab.
  :  is the bulk energy per atom.
  :  is the surface area.
  For a slab, we have two surfaces and they are of the same type, which is reflected by the number 2 in the denominator. To guarantee this, we need to create the slab carefully to make sure that the upper and lower surfaces are of the same type.
  Strength of adhesive contacts is determined by the work of adhesion which is also called relative surface energy of two contacting bodies. The relative surface energy can be determined by detaching of bodies of well defined shape made of one material from the substrate made from the second material. For example, the relative surface energy of the interface "acrylic glass – gelatin" is equal to 0.03 N/m. Experimental setup for measuring relative surface energy and its function can be seen in the video.